The present invention concerns a mechanical chuck for holding the shank of a tool in a hollow receiver in which a pull rod is disposed. By "tool" is meant a tool per se, or a tool holder, or other elements having a shank.
In a prior art chuck device a pull rod (or tension element) is centrally disposed in the tool receiver, the end surface of the pull rod being conical. Pins have one end lying on this conical surface. The pins project through the receiver, that is in the form of a cylindrical journal, from the interior outwards, and the other ends of the pins contact a conical surface of a hollow shank connected to the tool. Under tension, the conical end section of the pull rod forces the pins outwards in an essentially radial direction with a small axial component, so that the pins make contact with the conical inner surface of the hollow shank and move this shank in an axial direction over the journal until a stop is reached.
In the present invention, it is regarded as being disadvantageous that one must have direct or indirect access to the pull rod from the reverse side of the receiver in relation to the tool, in order to be able to move this pull rod in an axial direction. This requires a central through-boring of corresponding power transmission elements. However, it must be ensured that the pull rod also remains constantly under tension in the case of a rotating spindle. The shank formed as a trunnion is pushed away from the pins by relatively strong radial force components, which can adversely affect the exact fit of the shank in the receiver.
There are other well-known chucks in which the shank receiver is formed from a hollow element such that it can also receive the shank of a tool together with the pull rod. Thus, the afore-mentioned problems of fitting, that can arise with the use of a hollow shank, are compensated for, because the shank has a generally conical outer surface which enters an inner surface of the receiver, whereby the generally conical surfaces (e.g., abruptly beveled shanks) provide for an exact fit.
Nevertheless these other well-known chucks require access from the rear side of the receiver, so that the pull rod can be operated.
In addition to the above-mentioned chuck, there are also well-known simple drilling machine chucks, for example, in which clamp elements extending outwards are squeezed together by a clamping nut and thereby hold a drill shank or the like. These kinds of chucks are however relatively inaccurate, as they exert an axial strain on the shank to be held, which, just like the corresponding receiver, has no precisely defined surface that defines the exact reproductable fit for the shank or tool by lying one on the other.